A number of different video encoding standards have been established for encoding digital video sequences. The Moving Picture Experts Group (MPEG), for example, has developed a number of standards including MPEG-1, MPEG-2 and MPEG-4. Other examples include the International Telecommunication Union (ITU) H.263 standard, and the emerging ITU H.264 standard. These video encoding standards generally support improved transmission efficiency of video sequences by encoding data in a compressed manner. Compression reduces the overall amount of data that needs to be transmitted for effective transmission of video frames.
The MPEG-4, ITU H.263 and ITU H.264 standards, for example, support video encoding techniques that utilize similarities between successive video frames, referred to as temporal or Inter-frame correlation, to provide Inter-frame compression. The Inter-frame compression techniques exploit data redundancy across frames by converting pixel-based representations of video frames to motion representations. Frames encoded using Inter-frame techniques are referred to as P (“predictive”) frames or B (“bi-directional”) frames. Some frames, or macroblocks (MBs) within a frame, are encoded using spatial, Intra-frame compression, which is non-predictive. An Intra-coded frame is typically referred to as an I (“Intra”) frame.
Transmission of video data over a wireless network can be unreliable due to channel loss. Errors resulting from channel loss can adversely impact the quality of video presented to a user. In particular, channel errors can reduce not only the quality of a current frame, but also subsequent Inter-coded frames generated from the current frame using motion estimation and compensation techniques. To limit propagation of channel-induced errors from one frame to another, a video encoder typically applies an Intra-refresh (IR) technique. According to IR techniques, MBs within a P frame are selectively Intra-coded, rather than Inter-coded. Intra-coded MBs can improve error resilience, but require an increase in the number of bits that must be transmitted. Therefore, the IR rate impacts encoding performance in terms of both error resilience and bandwidth efficiency.